The wearing of sailor suits by anyone besides an actual sailor probably originated with young Prince Edward in the mid 19th century. He later had his own children dressed in miniature sailor uniforms.  A photograph of the children inspired a trend of dressing small boys in sailor suits - a trend that lasted well into the 20th century.  This illustration is from a 1908 catalog.

Around 1880, women's sport blouses began sporting sailor type collars. This type collar was soon used on bathing suits and gymnasium uniforms as well.  This was not a true middy, as it was designed to be tucked into, buttoned onto, or attached to the skirt or bloomers.  Illustration from 1908.

Sometime around 1910 the sailor blouse was developed into a true middy.  The middy did not "blouse" over the waist; it hung straight from the shoulders to the hips.  1916 Chicago Mail Order ad.

An important part of the middy was the fabric used.  The middy was constructed of cotton duck, like a sailor's warm weather middy. 1917 Paul Jones ad.

This box of Edwardian Christmas crackers is decorated with boys wearing middies.

Group of children in Finland, circa 1920

Thanks to Poppy's Vintage Clothing for the use of her photos.

Because of its practically, the middy quickly became standard wear for sports, gym and camp.  1919 ad.  Paul Jones was the brand name of Morris and Company, who claimed to be the originators of the middy.

In 1920 Camp Keystone (located in nearby Brevard, North Carolina and still in operation) required each camper to have at least eight white middies.

This photo is of a gym class at Mars Hill College, North Carolina, circa 1923.

By 1922, middies were not just for active sports.  They had crossed over into being a fashion item as well.  Dresses with middy tops became popular for spectator sports.  1922 Butterick Pattern Book.

The 1922 Montgomery Ward catalog had a full page of middies for young women, in various styles and colors.

Here are two fashion middies from the same company, Hofflin of Norfolk, Virginia.

This middy and skirt is identical to the one at left except for the color.

Thanks to dorotheasclosetvintage.com and materialgirlbags.com for the use of their photos.

The middy was worn over huge bloomers when used for sport.  The bloomers were commonly made from wool, but increasingly as the 1920s progressed, they too were made from cotton duck.

There were quite a few makers of middies, and companies were always coming up with improvements and variations. 

Here is the typical gym set:  white duck middy and blue cotton bloomers.

Sailor suits continued to be popular wear for little boys.  This one dates from 1922.

By 1929, the middy was pretty much back in its old position of being active sportswear.  Whereas in 1922 Montgomery Ward had a full page of middies, in 1929, there was just this one middy offered, and it was in the sports section instead of the clothing.

In an 1930s catalog, there was just this one middy-like blouse.  Bloomers were going, shorts were coming.

Even as late as 1931, though, middies were still being worn, as this McCall pattern dated 1931 shows.

Increasingly, the gymsuit was sleeveless and collarless.  This early 1930s gymsuit still has the V neck and the long straight bodice of the middy.

The middy has resurfaced from time to time as a fashion item.  They became popular as patriotic dresses during WWII.  Ladies Home Journal, 1941.

Here's a late 1950s middy and sailor-inspired blouse.

The dropped waist middy dress was brought back by Laura Ashley in the 1980s.